The present invention relates generally to electrical ballasts for energizing vapor lamps, and particularly to a ballast which may be used to energize a number of fluorescent lamps when powered by an AC line, but which exhibits substantially less power loss than the known, conventional ballasts.
Conventional ballasts such as, for example, type 446-LR-TC-P, manufactured by Universal Ballast Engineering, include a core about which a first winding arrangement is provided for connection to a 117 VAC (nominal) line, to produce exciting voltage and operating current for a pair of fluorescent lamps (e.g., a pair of 40 watt, type F40-T12/RS lamps). The first winding arrangement usually forms an autotransformer wherein a primary winding has a pair of leads for connection to the AC line, and a secondary winding is connected at one end to the primary winding and at the other end to a power factor correction capacitor which is typically about 3.7 to 4 microfarads. The conventional ballast also includes a second winding arrangement, including typically three separate filament heater windings for connection to filament heaters contained at each end of each of the fluorescent lamps. The remaining terminal of the power factor correction capacitor then is connected to one lead of one of the heater windings, and the same heater winding lead also is coupled to a lead of a different heater winding by a starter capacitor which is typically 0.05 microfarads.
AC power measurements at the primary winding of the type 446-LR-TC-P ballast reveal that with an AC line voltage of 117 volts, the ballast consumes 92 watts, while a pair of type F40-CW-T12/RS fluorescent lamps wired to the ballast emit 62 foot-candles of light at one meter distance on center. Inasmuch as a pair of 40 watt lamps ideally should consume only 80 watts of power, it will be understood that the additional 12 watts (92 minus 80) measured at the primary winding of the conventional ballast represents an appreciable power loss.